BER and MER are the two main parameters that provide an overall indication of the transmitted signal quality.
The bit error ratio (BER) is the number of bit errors divided by the total number of transferred bits during a studied time interval or a total number of bits. Though the time interval or the total number of transferred bits might be application specific, the commonly used in the communication industry metric is "Number of errors per million bits". AVQ1020 in the current configuration does not provide BER measurements.
The modulation error rate (MER) is calculated as an error vector between an ideal constellation point of the ideal and actually received signal. AVQ1020 averages MER (or SNR - signal-to-noise ratio) over approximately 40 symbols as reported on the main page of the web interface. MER parameter includes all signal imperfections and, therefore, is the main indicator of the transmitted signal quality. Drops in MER measurements should alarm broadcast engineers to analyze potential sources of signal degradation.
AVQ1020 keeps an internal "Variation Log" file which can be downloaded from the unit for further analysis - for averaging over greater period and/or studying SNR/MER variations over the time.